Under MacOSX, only set PLOW_THREADS to hyperthread amount if requesting max cpus
Under MacOSX, only set PLOW_THREADS to hyperthread amount if requesting max cpus

Br3nda/plow,Br3nda/plow,chadmv/plow,Br3nda/plow,chadmv/plow,Br3nda/plow,chadmv/plow,chadmv/plow,Br3nda/plow,chadmv/plow,chadmv/plow,chadmv/plow